The invention relates to a can; to a process for manufacturing the can; to a diaphragm for the closing and sealing thereof; and finally to a device for the manufacture of the diaphragm.
The prior art can is described in EU-A 007 487, but in practice it has never become known because on the one had the process described for the manufacture thereof required too great an effort, and on the other hand it did not function at all. Namely, in the aforementioned letters patent it was proposed that the collar part of the closing diaphragm to first be reduced in thickness or perforated by means of hard pressing surfaces along a circumferential line to serve later as a severance point, then to insert the diaphragm in the can opening, to heat it and to separate the diaphragm collar and the edge covering by the application of a pressure acting radially to the outside, along or next to the severance line. Apart from this process, which is complicated and susceptible to trouble, in practice a really complete separation of the two diaphragm parts has never been achieved, so that when the can was opened by tearing open the diaphragm dish, parts of the covering part were always pulled out along with the dish and frayed. Hence, precisely the effect occurred that the invention intended to avoid.
Another proposal is described in DE-A 32 12 990, but it could also not be realized in practice. There, the diaphragm consists of two layers; only the inner layer of the diaphragm dish rim is separated from the attendant edge covering, while the outer layer enwraps the dish and the edge covering without injury and serves for tearing open. It is as good as impossible to match the adhesive strength of the inner layer on the inside of the can to that of the two foils such that the effect that is endeavored by the invention is achieved--this due to contradictory requirements: in the dish area the adherence of the two foils on top of one another must be greater than the adherence of the collar of the inner layer on the inside of the can; in the coverage area it would have to be exactly the opposite in order that the inside foil covers the cut edge of the wall of the can with surety even after the tearing open.
The invention therefore has as its objective to devise a can of the type mentioned above that avoids the aforementioned disadvantages and that can be realized in practice. A can design in such a manner can be manufactured easily and poses no tearing-open problems, but rather leaves a smooth and clean covered part.
In accord with a further objective of the invention a process is to be devised with which the can can be closed and sealed in as simple a manner as possible, preferably in a single production operation, while achieving the endeavored advantages.
It is moreover the objective of the present invention to devise a diaphragm for closing and sealing cans or similar containers that can be made in a single operation, and that still provide easy opening by means of suitable severance points. This objective is achieved by the present invention by means of cut-outs and ligaments being provided alternatingly in the wall along a circumferential lines.
Finally, it is the objective of the present invention to devise a process and a device for the rational manufacture of the diaphragm according to said invention that is used for making a can that is closed and sealed according to the present invention.
A ligament in the diaphragm according to the present invention has a length of about 1 to about 30%, preferably 3 to 20%, especially 5 to 15% of the cut-out, preferably 6 to about 12, especially 8 to 10 cut-outs and ligaments being provided, depending on the diameter of the diaphragm. Fewer (longer) cut-outs and/or shorter ligaments endanger the workability of the diaphragm when it is being glued into the can because the long cut-outs tend to pull apart. More (shorter) cut-outs and/or longer ligaments incur greater problems on tearing open. The correct selection can easily be made by any person skilled in the art in function especially of the diaphragm material thickness and stiffness, as well as of the tolerances of the can.
In order that the diaphragm can be sealed in the can dependably it is expedient for the severance line to extend above half height of the wall, e.g. in the upper third thereof. To facilitate the tearing of the ligaments during the sealing they are preferably already pre-bent and/or even reduced in thickness--at least over a part of their width--so that they form severance points that actually tear on the application of a pull, while retaining the sealing of the edge covering. It is especially expedient for the ligaments to have a nearly fusiform cross-section by their two ends at the ends bordering on the respective cut-outs being crushed or slit to zero thickness.
In order to be able to manufacture such a diaphragm with an integral severance point in such a simple manner, according to a further embodiment of the invention a deep-drawing die and a matrix are used, each having a shearing edge all round for making the cut-outs. At least the shearing edge of one part of the tool is interrupted on the circumference, preferably at uniformly distributed locations.